The objective of this contract is to perform research leading to the development of a miniature tether-free electromechanically actuated implantable cardiac replacement system. An implantable cardiac replacement system as defined here includes biventricular support which assist the right and left ventricles which remain in situ and the total artificial heart which replaces the excised natural heart. The implantable subsystems of the replacement system include right and left heart blood pumps, and electromechanical energy converter(s), appropriate control systems, and implantable battery pack to provide short-term energy source for the system, a variable volume device and a mechanism for delivering electrical energy for outside to inside the body. The external battery pack will include electrochemical batteries, charging circuitry, and system monitor/diagnostic circuitry.